1. Field of the Invention
The present invention relates to a reverse break stamp hook assembly for use in breaking a biscuit from a casting and a method of breaking a biscuit from a casting using a reverse break stamp hook assembly.
2. Description of Related Art
The die casting process is used to produce accurately dimensioned, sharply defined, smooth and/or textured-surface metal parts. In the die casting process, molten metal such as, for example, aluminum and alloys of aluminum, is forced under high pressure into a cavity between two die halves. The injected molten metal quickly solidifies in the die cavity, then the two die halves are drawn apart and the casting is ejected.
The ejected casting typically includes extraneous material (e.g., flash, which is a thin web or fin of metal on a casting that occurs at die partings, vents and around moveable cores) that must be removed from the casting in order to obtain an acceptable part. In addition, castings formed using a cold chamber die casting machine will have a gate or biscuit, which is the excess of ladled metal remaining in the shot sleeve, that must be removed. The extraneous material and biscuit are typically removed in a stamping operation using a pair of trim dies and a die casting biscuit breaking apparatus. The trim dies include cutting/trimming surfaces as well as punches or other desired tooling.
FIGS. 1A and 1B show a schematic front view of a conventional die casting biscuit breaking apparatus 10. The apparatus 10 consists of an upper trim die holder 18, an upper trim die 20, a lower trim die holder 28, and a lower trim die 30. A part 40 (or several parts) is placed between the dies 20, 30, typically on the lower trim die 30. The part 40 will typically include extraneous material (e.g., flash) that needs to be trimmed, surfaces to be punched, as well as a gate or biscuit 50 that needs to be removed. As shown in FIG. 1 B, the upper trim die holder 18 is moved downwardly to press the upper trim die 20 against the part 40 on the lower trim die 30 and thereby trim away the extraneous material from the part 40. Conventionally, the upper trim die holder 18 also includes a stamp cutter 60 that presses downwardly against the biscuit 50 or gate to break the biscuit from the part 40.
One of the problems with a conventional die casting biscuit breaking apparatus 10 is that the biscuits 50 tend to break off a distance from the part 40, leaving a portion of biscuit material, sometimes referred to as a xe2x80x9chigh gatexe2x80x9d70, remaining on the part 40. These high gates 70 must be removed by hand, typically using angle grinders. This results in additional processing time and effort. On occasion, a high gate 70 will not be noticed upon inspection or will be improperly removed by hand. An overlooked high gate 70 can cause damage to tooling in downstream processes, resulting in machine down time and additional losses in production time due to the need to hand sort parts to find the missed high gates 70.
The present invention provides a reverse break stamp hook assembly for use in breaking a biscuit from a casting, and a method of breaking a biscuit from a casting using the reverse break stamp hook assembly. Surprisingly, the reverse break stamp hook assembly and method according to the invention facilitate the removal of biscuits without creating a high gate. Moreover, the reverse break stamp hook assembly may be used with conventional stamping machines without modifying the operating sequence of the machine.
In accordance with the present invention, a reverse break stamp hook assembly is mounted in place of a stamp cutter on conventional stamping equipment. The reverse break stamp hook assembly includes a hook and a mounting bracket. The hook, which includes a downwardly extending leg and a counterweight arm, hangs from a pivot attached to the mounting bracket. A distal end of the hook leg has an angled front portion and a catch portion.
In further accordance with the present invention, as the upper trim die of the stamping equipment moves toward the lower trim die during the downstroke, the angled front portion of the hook contacts and slides over an edge of a biscuit, causing the hook to pivot away from the biscuit until the catch portion passes below the biscuit. The counterweight arm, which is on the opposite side of the pivot, causes the hook to pivot back toward the biscuit, positioning the catch portion under the biscuit. During the upstroke, the catch portion engages the bottom side of the biscuit and pulls the biscuit upwardly away from the part, causing the biscuit to break from the part as the upper trim die is raised. The biscuit breaks cleanly, and does not leave a high gate requiring further hand grinding. Accordingly, a rough cleaned and trimmed part results from use of the trim dies incorporating the reverse break stamp hook assembly of the present invention.